A piglet model of status epilepticus: comparison of cardiorespiratory and metabolic changes with two methods of pentylenetetrazol administration.

Abstract

Impaired cardiac and respiratory responses during active tonic-clonic convulsions (ictal periods) may contribute to complications during seizures. This study characterized physiologic parameters in two pentylenetetrazol (PTZ)-induced seizure models. Twelve spontaneously breathing piglets. Under ketamine anesthesia, a tracheostomy was performed, and an arterial catheter and epidural electrodes were inserted. Piglets received a PTZ bolus (100 mg/kg), with (six; 5 mg/kg/min) or without (six) an infusion of PTZ for 20 minutes. Arterial blood gases, mean arterial pressure, heart rate, tidal volume, and EEG waveforms were measured. Ictal periods had high-amplitude, synchronized EEG activity; interictal periods had EEG suppression. Seizure duration (24 +/- 3.5 versus 11 +/- 3.8 minutes; mean +/- SD) was significantly increased in the infusion group (P < .05). Significant increases in heart rate, minute ventilation, and base deficit plus decreases in pH occurred in both groups during seizures compared with baseline (P < .05). The duration and severity of metabolic acidosis were greater in the infusion group. During the first ten minutes of seizures, ten-second epochs were compared: beginning of ictal period, end of same ictal period, beginning of accompanying interictal period, and end of same interictal period. Respiratory rate decreased during initial interictal (65 +/- 40) more than latter ictal more than latter interictal period, compared with initial ictal period (194 +/- 65; P < .001). Tidal volume increased during latter ictal more than latter interictal more than initial ictal period (33 +/- 11), but the greatest increases occurred during initial interictal period (140 +/- 55; P < .001). This model demonstrates significant increases in the duration and various measures of seizure severity in piglets given a PTZ infusion compared with those receiving a bolus alone. Systematic alterations in respiratory but not cardiac responses occur during ictal-interictal cycling of PTZ-induced seizures.